Arrangement for damping linear movements

ABSTRACT

Arrangement for damping linear movements intended for use on a safety valve. An arrangement for damping linear movements of the valve spindle (10) of a safety valve of small amplitude and high frequency comprises two counter-rotatable damping parts (18, 36) with intermeshing wall (22, 24, 32) which delimit narrow working gaps (44, 46) containing a high-viscosity silicone grease. The linear intake movement is converted by a threaded drive (12, 40) into a rotary movement during which the silicone grease (47) in the working gaps (44, 46) is subjected to shear forces and eliminates the unwanted energy by virtue of its internal friction.

DESCRIPTION

The invention relates to an arrangement for damping linear movements foruse on a safety valve.

A damping arrangement of this type is described in FR-A No. 2 389 047.

In the latter, two cup-shaped damping parts, which together define aworking gap filled with a viscous medium, have a fixed, predeterminedaxial position.

If one were to use a damping arrangement of this type on a safety valve,then the damping would not be satisfactory, since the damping comes intoaction reliably on the one hand already at very small openingdisplacements of the closure part, irrespective of manufacturingtolerances, which result for example from the machining of the sealingsurfaces. Also, in safety valves of this type, the force acting on thevalve spindle also varies very considerably depending on the openingdisplacement and the known damping arrangement thus cannot damposcillations, which occur in the immediate vicinity of the closingposition, as well as other oscillations which are set up around a partlyopen position.

The present invention therefore intends to develop an arrangement fordamping linear movements so that the damping characteristics can beadjusted precisely in a simple manner.

This object is achieved according to the invention by a dampingarrangement C.

Advantageous developments of the invention are described in theSub-claims.

In another damping arrangement, the value of thedisplacement-independent component of the damping can be adjusted in avery simple manner. One can thus adjust the damping properties of thesafety valve easily at the installation point taking into considerationthe lengths of the pipe sections connected to the safety valve at theinlet side and the outlet side.

In a damping arrangement according to another embodiment, a smalldisplacement-dependent component of the damping can be adjusted, thiscomponent being progressive or degressive according to the pitch of thesupport-screw coupling.

The development of the invention according to another embodiment is anadvantage with regard to the lowest possible abrasive nature of theviscous medium.

The invention will be described in detail hereafter by means ofembodiments, referring to the drawings, in which:

FIG. 1 is an axial section through a damping arrangement for a valvespindle operating with a viscous medium; and

FIG. 2 is a similar sectional view to FIG. 1, in which a modifieddamping arrangement is illustrated.

FIG. 1 shows the upper end of a valve spindle 10, which is provided witha threaded section 12. The valve spindle is guided on a valve housing byway of sliding packings (which are not shown in detail) and at its lowerend not shown in the drawing supports a closure member, whichco-operates with a valve seat likewise not shown.

Of the valve housing, only an upper end section of the housing 14 isshown, which receives a damping arrangement acting on the valve spindle10 and designated generally by the reference numeral 16.

Belonging to the damping arrangement 16 is a lower damping part 18,which comprises a transverse base 20 and two working walls 22, 24coaxial with respect to the axis of the valve spindle 10.

The base 20 is clamped between two threaded rings 26, 28, whereof theexternal threads engage in an internal thread 30 of the end section ofthe housing 14.

Engaging between the working walls 22, 24 in the manner of a comb is afurther working wall 32, which is supported by a hub section 34. Thecomponents 32 and 34 together form an upper damping part 36.

The damping part 36 is mounted by way of an axial/radial bearing 38 onthe end section of the housing 14.

The hub section 34 is provided with an internal thread 40, whichco-operates with the threaded section 12 of the valve spindle 10.

The annular space defined by the working walls 22, 24 is filled with ahighly viscous silicone grease 42. The latter contains graphite as afiller component or as the exclusive filler. The level of the siliconegrease 42 extends above the lower edge of the suspended working wall 32of the upper damping part 36.

The inner surface of the working wall 24 and the outer surface of theworking wall 32 as well as the inner surface of the working wall 32 andthe outer surface of the working wall 22 form two pairs of workingsurfaces, between which the annular working gaps 44, 46 are located. Athin layer of silicone grease 42 is located in these working gaps. Thethickness of the working gaps is illustrated in an exaggerated manner inthe drawing; in practice the thickness of the gap amounts toapproximately 0.1 to approximately 1 mm.

If the valve spindle 10 is moved in a linear manner, for example due topressure surges acting on the closure member in the pipe to beprotected, then the linear movement of the valve spindle 10 is convertedby a movement conversion transmission, which is formed by theco-operating threads 12 and 40 as well as the axial/radial bearing 38,into a pure rotary movement. This rotary movement leads to shearing ofthe silicone grease 42 located in the working gaps 44, 46, and due tothe inner friction of this highly viscous medium, the movement of thevalve spindle 10 is damped.

It can be seen that irrespective of the distance covered by the valvespindle 10, one has exactly the same working gap geometry, so that thedamping of the movement takes place independently of the displacement.

The embodiment illustrated in FIG. 2 corresponds largely to thataccording to FIG. 1, so that corresponding components have again beengiven the same reference numerals and are not described again in detailhereafter.

The upper damping part 36 is now not mounted by way of an axial/radialbearing, but by way of an external thread 48 on the hub section 34 and amatching thread 50 integral with the housing, on the end section of thehousing 14. Compared with the treaded section 12 of the valve spindle10, the threads 48 and 50 have a small pitch so that for a given axialmovement of the valve spindle 10, one obtains only a small axialadjustment of the upper damping part 36, thus also a small variation ofthe penetration depth of the working wall 32 into the silicone grease42. In this case, this variation of the penetration depth may bepositive or negative, according to whether the pair of threads 48, 50has the same direction of rotation as the pair of threads 12, 40 or theopposite direction of the rotation. The extent of thedisplacement-dependent portion of the damping can be adjusted by way ofthe pitch of the threads 48, 50.

In the case of both above-described damping arrangements, the intensityof the basic damping can be predetermined by adjusting the lower dampingpart 18, for which purpose the threaded rings 26, 28 are appropriatelyscrewed on the internal thread 30 of the end section of the housing 14.

Both above-described damping arrangements operate completely withoutstatic friction. One thus has effective damping even for low oscillationamplitudes, damping taking place in a speed-dependent manner.

I claim:
 1. An arrangement for damping linear movement for use on asafety valve, said safety valve including(a) a housing (14), a valveshaft (10) to be connected to a valve element to be damped, (c) an outercup-shaped damping part (18) mounted within said housing (14), (d) arotary inner cup-shaped damping part (36) located within said housing(14) and extending into said damping part (18) from above, the outersurface of said damping part (36) together with the inner surface ofsaid damping part (18) defining a working gap in which a viscous medium(42) is located, (e) a movement-conversion transmission means (12, 38,40) for converting the linear movement of the valve shaft (10) into arotary movement of said rotary inner damping part (36), and (f) meansfor adjusting the axial relative positions of said damping part (18) andsaid rotary inner damping part (36) to thereby adjust the depth ofimmersion of the said rotary damping part (36) in said damping part (18)and to thereby control the dampening intensity for the valve element. 2.A damping arrangement according to claim 1, wherein said damping part(18) is supported on the housing (14) by way of a threaded connection(26 to 30).
 3. A damping arrangement according to claim 1 wherein therotary damping part (36) is supported on the housing (14) by that of athreaded connection (48, 50).
 4. A damping arrangement according toclaim 1 wherein said movement-conversion transmission means comprises athread (12) formed on the axially moveable valve shaft (10), which isfixed in the angular direction, and a thread (40) engaging therewith andconnected to the rotary damping part (36).
 5. A damping arrangementaccording to claim 1 wherein the movement-conversion transmissioncomprises a helical cam groove formed in the spindle and a camcooperating therewith and connected to the rotary damping part (36). 6.A damping arrangement according to claim 1 wherein the viscous medium isa silicone grease containing a filler, the filler consisting at leastpartly of graphite.
 7. A damping arrangement according to claim 1wherein the viscosity of the viscous medium does not vary substantiallyover a large temperature range.
 8. A damping arrangement according toclaim 1 wherein the working gaps between the damping parts (18, 36), inwhich the viscous medium (42) is located, have a width of less thanapproximately 1 mm.